... by implementing some kind of recalloc (mix of realloc and calloc).

Fixes this valgrind finding:

==7061== Syscall param writev(vector[...]) points to uninitialised byte(s)
==7061==    at 0x781EFE0: __writev_nocancel (syscall-template.S:84)
==7061==    by 0x488974: _XSERVTransSocketWritev (Xtranssock.c:2914)
==7061==    by 0x47DBD3: FlushClient (io.c:1080)
==7061==    by 0x47DBD3: FlushAllOutput.part.0 (io.c:817)
==7061==    by 0x477304: WaitForSomething (WaitFor.c:246)
==7061==    by 0x434369: Dispatch (NXdispatch.c:360)
==7061==    by 0x40EB92: main (main.c:353)
==7061==  Address 0x102106f3 is 50,211 bytes inside a block of size 54,308 alloc'd
==7061==    at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7061==    by 0x47F08F: FlushClient (io.c:1123)
==7061==    by 0x47F307: WriteToClient (io.c:991)
==7061==    by 0x42903C: doListFontsAndAliases (NXdixfonts.c:660)
==7061==    by 0x42B7D6: ListFonts (NXdixfonts.c:735)
==7061==    by 0x433A6D: ProcListFonts (NXdispatch.c:989)
==7061==    by 0x4344A5: Dispatch (NXdispatch.c:482)
==7061==    by 0x40EB92: main (main.c:353)
==7061==  Uninitialised value was created by a heap allocation
==7061==    at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7061==    by 0x47F08F: FlushClient (io.c:1123)
==7061==    by 0x47F307: WriteToClient (io.c:991)
==7061==    by 0x42903C: doListFontsAndAliases (NXdixfonts.c:660)
==7061==    by 0x42B7D6: ListFonts (NXdixfonts.c:735)
==7061==    by 0x433A6D: ProcListFonts (NXdispatch.c:989)
==7061==    by 0x4344A5: Dispatch (NXdispatch.c:482)
==7061==    by 0x40EB92: main (main.c:353)
==7061==